Keyboard switch

ABSTRACT

A switch case has a top provided with a central opening in which slides the stem of a plunger that has a foot inside the case and a cap on its upper end. A spring normally holds the plunger in its upper position with its foot adjacent the top of the case. The foot carries a bridging contact formed from a spring having free end portions extending away from the opposite sides of the foot to form movable contacts that engage stationary contacts in the case when the plunger is depressed.

United States Patent 1 Sykora 1 Oct. 23, 1973 [54] KEYBOARD SWTCHFOREIGN PATENTS OR APPLICATIONS [751 invent: Allan sykol'a, Cary,1,248,967 11 1960 France 200/159 R [73] Assignee: Stackpole ComponentsCompany,

Raleigh NC Primary Examiner-J. R. Scott I Assistant ExaminerRobert A.Vanderhye [22] Flled: Sept 1972 AttameyBrown, Murray, Flick & Peckham 21Appl. No.: 290,980

[57] ABSTRACT 52 vs. 01. 200/159 R 200/166 BA A Switch case has aPwvided with a central 51 int. Cl 110111 13/S 2,H01h 1/24 mg whiihSlides the stem Plunge that has a 581 Field Of Search 200/159 R 159 Ainside the case and a cap on its upper A 200/166 BA spring normallyholds the plunger in its upper position with its foot adjacent the topof the case. The foot [56] References Cited carries a bridging contactformed from a spring having free end portions extending away from theopposite 6 U T S PATENTS sides of the foot to form movable contacts thatengage l stationary contacts in the case when the plunger is de- 1ams ea 2,567,42l 9/l95l Brantingson 200/159 A presse 2,727,955 12/1955 Brown200/159 R X 6 Claims, 6 Drawing Figures KEYBOARD SWITCH This inventionrelates to keyboard switches suitable for use in calculators, dataprocessing and stock quotation equipment, cash registers,- audio-visualeducation equipment, communication equipment, typewriters and otherdevices. I

It is among the objects of this invention to provide a keyboard switchof simple and inexpensive construction, which has a long life and anextremely small bounce that remains uniform throughout the life of theswitch.

The preferred embodiment of the invention is illustrated in theaccompanying drawings, in which FIG. 1 is a vertical section of the openswitch;

FIG. 2 is a view at 90 to FIG. 1, with part of the switch case brokenaway;

FIG. 3 is a fragmentary vertical section similar to FIG. 1, but with theswitch closed;

FIGS. 4 and 5 are horizontal sections taken on the lines lV-IV and V--V,respectively; and

FIG. 6 is a fragmentary bottom view of a panel supporting the switch.

Referring to FIGS. 1, 2 and 5 of the drawings, a rectangular case 1,generally molded from a plastic, has in its top wall a central verticalopenings, from which a cylindrical flange 2 extends upwardly a shortdistance. The bottom wall 3 of the case may be attached to the rest ofthe case by downwardly extending lugs 4 that project through slots inthe bottom wall. The lower ends of these lugs can be deformed by heat tolock the bottom wall in place. The bottom of the case is provided with acentral vertical post 5 designed to have a press fit in a printedcircuit board or other panel 6 on which the switch can be mounted. Thepost holds the switch in place.

The stem ofa plunger 7 is slidably mounted in the top wall opening andflange 2 of the case and extends above the flange. The lower end of thestem inside the case is provided with a foot 8 that normally is heldagainst the top wall of the case by means ofa coil spring 9 encirclingthe plunger and compressed between the case and a cap 10 frictionallymounted on the upper end of the plunger and always spaced from the case.

The foot of the plunger carries a bridging contact inside the case. Itis a feature of this invention that the bridging contact is a springattached to the plunger foot and having free end portions extending awayfrom opposite sides of the foot to form movable contacts. Preferably,this contact spring is formed from a spring wire coil 12 that extendsacross the plunger foot as shown in FIG. 4. The coil is disposed in adownwardly opening transverse slot 13 in the foot. The opposite endportions of the coil are more or less straight and extend tangentiallyaway from opposite sides of the bottom of the coil to form the movablecontacts 14 of the switch, as shown in FIG. 1. These free end portionsor contacts will constantly press downwardly if they are pressedupwardly relative to the axis of the coil by stops 15 formed byextending beneath the contacts diagonally opposite lower corners of theside walls of the slot. With this construction the contacts press downagainst the stops and extend away from them towards the opposite ends ofthe case.

To help guide the foot of the plunger in the case so as to prevent itfrom turning, the foot preferably is provided with guide lugs 17extending away from the opposite side walls of slot 13 in substantiallyparallel '2 spaced relation with the movable contacts 14, as shown inFIG. 4. These guide lugs project beyond the ends of the contacts andinto sliding engagement with the end walls of the case. Preferably, theend walls are provided with guide slots 18 extending vertically acrossthem for receiving the ends of the lugs. Also, it is preferred that thelugs be located at diagonally opposite corners of the foot of theplunger. 7

The inside of the case is provided with a pair of fixed or stationaryelectric contacts 20 normally spaced beneath the movable contacts and intheir paths. Most conveniently, the stationary contacts project upwardlyfrom the bottom wall of the case. Also, it is preferred to make thesestationary contacts integral with the terminals 21 that project from thebottom of the case. Thus, each stationary contact can be the exposedwide head of narrow terminal that extends down through an opening in thebottom wall of the case. The contact and terminal can be held firmly inplace by providing the portion of the terminal inside the wall openingwith teeth that tightly engage the sides of the opening.

When the cap 10 is pressed to depress the plunger, the bridging contactis moved downwardly in the case and the spring wire movable contacts 14engage the stationary contacts below them as shown in FIG. 3. Althoughone movable contact may engage the underlying stationary contact shortlybefore the other two contacts come into engagement, the plunger movesdown far enough to ensure that both sets of contacts will engage firmly.Since both ends of the spring wire coil are pressed against thestationary contacts, the pressure of the two movable contacts againstthe stationary contacts is equalized because the coil is free to turn onits axis to the extend necessary for pressure equalization.

With the keyboard switch disclosed herein, it has been found that thebounce is less than 1 millisecond, which is an acceptable figure forsuch a switch. Bounce duration much greater than this might possiblycause a double signal.

As shown in FIG. 6, the panel into which the switch post 5 is insertedis provided with enlarged openings 23 for the switch terminals. Theseopenings allow the post to be turned in the panel sufficiently toproperly align the switch cap with like caps on the other switchesmounted on the same panel.

According to the provisions of the patent statutes, I have explained theprinciple of my invention and have illustrated and described what I nowconsider to represent its best embodiment. However, I desire to have itunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically illustrated anddescribed.

I claim:

1. A keyboard switch comprising a case having a top with a centralopening therethrough, a plunger having a foot in the case and a stemextending upwardly through said opening and above the case, a capmounted on the upper end of the plunger and spaced from the case, aspring normally holding the plunger in its upper position with its footadjacent the top of the case, the plunger foot having an openingextending across it, a spring wire coil extending across said foot insaid opening and having free end portions extending tangentially awayfrom opposite sides of the coil to form movable contacts, said footbeing provided with means holding the coil in said opening with themovable contacts spaced from the case, a pair of stationary electriccontacts mounted in the case beneath said movable contacts and normallyspaced therefrom, said movable contacts being engageable with thestationary contacts when the plunger is depressed by said cap, andterminals connected with the stationary contacts and extending out ofthe case.

2. A keyboard switch according to claim 1, in which said plunger foothas guide lugs extending in substantially parallel spaced relation withsaid free end portions of the bridging contact spring for slidingengagement with opposite side walls of the case.

3. A keyboard switch according to claim 2, in which said opposite sidewalls of the case have guide slots extending vertically across themreceiving said guide lugs.

4. A keyboard switch according to claim 1, in which said coil-holdingmeans are stops limiting downward movement of said movable contactsrelative to the plunger.

5. A keyboard switch according to claim 1, in which said foot opening isa downwardly opening transverse slot containing said coil, said free endportions extend laterally away from the bottom of the ends of the coilat opposite ends of said slot, and said coil-holding means are stopslimiting downward movement of said free end portions relative to theplunger.

6. A keyboard switch according to claim 5, in which said stops arediagonally opposite lower corners of the walls of said slot projectingbeneath said movable contacts.

2. A keyboard switch according to claim 1, in which said plunger foothas guide lugs extending in substantially parallel spaced relation withsaid free end portions of the bridging contact spring for slidingengagement with opposite side walls of the case.
 3. A keybard switchaccording to claim 2, in which said opposite side walls of the case haveguide slots extending vertically across them receiving said guide lugs.4. A keyboard switch according to claim 1, in which said coil-holdingmeans are stops limiting downward movement of said movable contactsrelative to the plunger.
 5. A keyboard switch according to claim 1, inwhich said foot opening is a downwardly opening transverse slotcontaining said coil, said free end portions extend laterally away fromthe bottom of the ends of the coil at opposite ends of said slot, andsaid coil-holding means are stops limiting downward movement of saidfree end portions relative to the plunger.
 6. A keyboard switchaccording to claim 5, in which said stops are diagonally opposite lowercorners of the walls of said slot projecting beneath said movablecontacts.